Google didn't invent adtech, the only thing you can credit them for is to have resisted from contracting a third party ad network and becoming an ad network on their own to be able to keep control on the form their ads take: read less annoying and intrusive: no image, no moving parts, only text thus not alienating their user base and killing their business as other website had been doing.

Funnily from here the primary fields for google seem to be surveillance, tracking, profiling, lobbying, tax evasion, abuse of dominant position, killing useful services people actually use, buying competitors to close them, killing other businesses by making a competitor product available with no price tag (you pay with your personal data being collected), evading anti-monopoly law, and other things in the same vein.

Ads on the Internet existed well ahead of Google. Google simply captured search intent and bought out DoubleClick.